I'm cheap, so I LOVE Spirit. It's ideal if you're only planning to travel with a backpack and don't really care about the timing of your flights. If you start adding on baggage and stuff, your pricing goes up, but I've only had good experiences with Spirit. Their employees have always been friendly and kind and I've never had any unexpected delays or issues.
I think, in many cases, Spirit is better than other airlines. Last time I flew American, they tried to separate me from my kids on the flight. They were two and five at the time. No joke. I literally had to talk to other people on the flight to see if any of them would switch so my kids could sit by me. Never in my entire life have I ever heard of something so outrageous. It's one thing if the flight attendant looks around and makes the arrangements, but to make the customer try to find a way to sit by their small children... Ugh. Never again. United left me stranded once too. When I was flying with my disabled mom. That was a real treat. They told us we could just wait at the airport for 24 hours. Like, really? They offered nothing in the way of solutions, no hotel vouchers, nothing. Just, "Sorry, you're screwed. Good luck with that." Bah.